The invention is directed to a method for splicing a conveyor belt having vulcanized rubber with steel strands embedded in the vulcanized rubber, comprising the steps of exposing a plurality of strands at two belt ends, and applying a vulcanizable rubber composition to the exposed strands to form a spliced joint between the two belt ends, the vulcanizable rubber composition comprising 100 parts by weight of rubber, and the rubber comprising from about 1 to about 20 parts by weight of syndiotactic polybutadiene.
Conveyor belts are commonly used as a means to move material from one location to another. In large mining operations, the conveyor belt is generally formed of a rubber body embedded with steel cords or strands. A cover compound can be used at the surface wherein the material is to be conveyed. Generally the compound is very abrasion and cut resistant and of sufficient thickness to prevent the rocks being conveyed from tearing the belt. A pulley compound can be used on the interior surface, this rubber is ideally suited for improved wear as the belt traverses over the pulleys used to drive the belt.
These steel corded or stranded belts may extend several miles and cost millions of dollars to install and fabricate. The fabrication of such belts occurs initially at a factory wherein steel strands or cords are arranged in a coplanar relationship parallel to the surface of the belt so that the belt will exhibit uniform expansion and minimize weaving as it traverses which can cause belt damage.
The prior art method of fabricating belts requires the steps of vulcanizing the rubber belt and winding it onto large spools for shipping to the site. Once the spools of belt are received at the site, the ends must be prepared for splicing by removing the vulcanized rubber from the strands over a distance determined to be sufficient to provide enough joint length to make a secure splice.
Removal of the rubber can be a very time consuming and tedious task. Often times piano wire is used to peel the vulcanized rubber from the strands. In large belts of several feet in width over a hundred strands must be exposed at each joint end. Once exposed, the strands had to be cleaned of as much of the vulcanized rubber as possible. The strands were then cleaned with solvents such as toluene and then a bonding agent was applied comprising a 3:2 mixed solution of xe2x80x9cChemlok No. 203xe2x80x9d and xylene, for example, and rubber cement is applied to the strands and dried. After the preparation of both ends as described in U.S. Pat. No. 3,487,871 entitled xe2x80x9cA METHOD OF JOINING CONVEYOR BELTS HAVING STEEL CORDS EMBEDDED THEREINxe2x80x9d granted Jan. 6, 1970, a joining member is formed made of vulcanized or semi-vulcanized rubber of the same quality as the rubber used in the formation of the belt. The upper face of the member is preferably made of a non-vulcanized rubber and provided with a plurality of strand receiving grooves. Once the strands are in place, a bonding agent of the type described above is preferably coated on the faces of the surfaces to insure complete bonding. While this prior art patent use the term xe2x80x9cnon-vulcanized rubberxe2x80x9d being preferable at the melting surfaces of the otherwise vulcanized or semi-vulcanized member (13), it is believed that the term means xe2x80x9chaving at least its upper surface formed of incompletely vulcanized rubberxe2x80x9d as was required in the claim of the patent. An important limitation when the member for splicing is semi-vulcanized at this grooved surface, the use of semi-cured rubber forced the use of bonding solvents. These solvents are high in VOC""s and the liberal use of xylene and toluene creates carcinogenic risks to the personnel. In developed parts of the world, the use of such solvents is greatly discouraged.
A second limitation of the prior art splicing member is that the member was apparently molded to the exact width of the belt and had exactly twice the number of strands as the belt. This meant that for each belt width, there had to be a unique member since conveyor belts are not standardized in width or in the size or in the number of strands to use the concept taught in that patent required specially designed molds.
A third limitation of the method of splicing described in U.S. Pat. No. 3,487,871 was that the strands had to be free of any of the vulcanized belt rubber which, if left on the strands, adversely affected the bonding.
An alternative method to solvent stripping method for splicing a conveyor belt is taught in PCT publication WO 00/53952, wherein a method of splicing the ends of conveyor belts having vulcanized rubber with steel strands embedded in the vulcanized rubber is disclosed. The method has the steps of
(A) removing a portion of the rubber from the belt ends to be joined exposing a plurality of strands;
(B) providing preformed unvulcanized strips of rubber, in an array of bottom strips each strip having a concave quarter-circular profile wherein strips when laid adjacently to each other form strand receiving grooves located on an upper surface;
(C) placing exposed strands of the belt ends being joined in the grooves of the bottom strip; and
(D) placing top strips overlying the array of bottom strips and vulcanizing the strips together thereby forming the spliced joint.
High modulus compounds have been proven to be necessary to increase the splice load capability of steel cable-reinforced conveyor belts. Steel cable-reinforced conveyor belts are graded relative to splice strength in a dynamic mode. Splice strength has historically been rated at 30 percent of cable breaking strength. Higher modulus compounds enable the splice rating to be increased into the 40 to 50 percent range.
Steel cable-reinforced conveyor belts are rated according to splice strength. This rating is determined by dynamically testing a belt under tension at a percentage of the total belt breaking strength. Customers now refer to this rating for purchasing decisions. It is desirable to develop novel splice methods utilizing rubber compounds that will allow the dynamic testing, commonly referred to as the Hanover test, to reach a higher number of cycles at a specific test load or a belt to be successfully tested at a higher load.
The invention is directed to a method for splicing a conveyor belt having vulcanized rubber with steel strands embedded in the vulcanized rubber, comprising the steps of exposing a plurality of strands at two belt ends, and applying a vulcanizable rubber composition to the exposed strands to form a spliced joint between the two belt ends, the vulcanizable rubber composition comprising 100 parts by weight of rubber, and the rubber comprising from about 1 to about 20 parts by weight of syndiotactic polybutadiene.